Identification and functional characterization of the CSF1R gene from grass carp Ctenopharyngodon idellus and its use as a marker of monocytes/macrophages

Characterization of two novel MCSFR paralogues in rainbow trout Oncorhynchus mykiss: New insights into the molecular mechanism underlying macrophage differentiation and modulation in fish

Colony-stimulating factor-1 (CSF-1) receptor, also known as macrophage colony-stimulating factor (MCSF) receptor, belongs to the type III protein tyrosine kinase receptor family. MCSF and IL-34 play essential roles in both innate and adaptive immune systems in vertebrates through their shared receptor MCSFR. While the functional study of MCSFR in mammals has been well-demonstrated, its role in fish remains limited. Therefore, this report aims to identify and study the expression of the MCSFR genes in rainbow trout Oncorhynchus mykiss, where four paralogues were found present at different genomic loci, two identified for the first time in this study. The deduced protein structure of these MCSFRs reveals five immunoglobulin (Ig)-like domains, a transmembrane domain and a conserved intracellular domain containing a glycine-rich motif (Gly-x-Gly-x-x-Gly), similar to other species. Phylogenetic and synteny analyses demonstrate that MCSFR are present throughout vertebrates, with two forms present in teleost fish more generally (type I and type II MCSFR), existing as pairs of genes (MCSFR1a/MCSFR1b, MCSFR2a/MCSFR2b) in trout. The MCSFR genes are widely expressed, with higher transcript levels observed in immune tissues such as the spleen, blood and head kidney. The paralogues showed marked differences in expression modulation. Following Yersinia ruckeri infection, MCSFR2a was highly induced but after stimulation of RTS-11 cells, a trout monocyte/macrophage-like cell line, with Y. ruckeri flagellin both MCSFR1b and MCSFR2a were induced. However, none of the different paralogues of MCSFR were induced by proinflammatory cytokines (trout rTNF-α, rIL-6 and rIFN-γ). This study adds to our knowledge of the molecules/pathways present in fish that drive macrophage regulation and activation, and emphasizes the complexity present with multiple ligands and receptors involved.

Single-nuclei transcriptome analysis of channel catfish spleen provides insight into the immunome of an aquaculture-relevant species

The catfish industry is the largest sector of U.S. aquaculture production. Given its role in food production, the catfish immune response to industry-relevant pathogens has been extensively studied and has provided crucial information on innate and adaptive immune function during disease progression. To further examine the channel catfish immune system, we performed single-cell RNA sequencing on nuclei isolated from whole spleens, a major lymphoid organ in teleost fish. Libraries were prepared using the 10X Genomics Chromium X with the Next GEM Single Cell 3' reagents and sequenced on an Illumina sequencer. Each demultiplexed sample was aligned to the Coco_2.0 channel catfish reference assembly, filtered, and counted to generate feature-barcode matrices. From whole spleen samples, outputs were analyzed both individually and as an integrated dataset. The three splenic transcriptome libraries generated an average of 278,717,872 reads from a mean 8,157 cells. The integrated data included 19,613 cells, counts for 20,121 genes, with a median 665 genes/cell. Cluster analysis of all cells identified 17 clusters which were classified as erythroid, hematopoietic stem cells, B cells, T cells, myeloid cells, and endothelial cells. Subcluster analysis was carried out on the immune cell populations. Here, distinct subclusters such as immature B cells, mature B cells, plasma cells, γδ T cells, dendritic cells, and macrophages were further identified. Differential gene expression analyses allowed for the identification of the most highly expressed genes for each cluster and subcluster. This dataset is a rich cellular gene expression resource for investigation of the channel catfish and teleost splenic immunome.

A cytokine-like factor 1 homolog acts as a macrophage chemoattractant in grass carp

Cytokine-like factor 1 (CYTL1) is a small cytokine and has diverse biological functions in mammals. However, whether CYTL1 exists in lower vertebrates is not clear. In this study, we identified cytl homologs in fish and characterized the immune functions in a teleost species, grass carp (Ctenopharyngodon idella). Fish CYTL1 homologs share conserved molecular features with their mammalian counterparts, including 6 cysteine residues in the mature peptide, genomic organization and synteny. Gene expression analysis revealed that cytl1 was constitutively expressed in tissues of grass carp, with the highest expression detected in the heart. Upon infection with Aeromonas hydrophila (A. hydrophila), cytl1 was downregulated in the hindgut, head kidney, skin, and spleen. In the primary head kidney leukocytes (HKLs), stimulation with inactivated A. hydrophila, LPS, poly(I:C), IL-22, IFN-a or IFN-γrel resulted in downregulation of cytl1 expression. Recombinant grass carp CYTL1 protein produced in the HEK293-F cells was potent to induce il-10 expression, but had little effect on the expression of il-1β and il-6. In vivo experiments revealed that CYTL1 was effective to recruit macrophages to the muscle injected with cytl expression plasmids. Taken together, our results indicate that CYTL1 is a potent chemokine for recruitment of macrophages in fish.

Blunt snout bream (Megalobrama amblycephala) MaCSF-1 contributes to proliferation, phagocytosis and immunoregulation of macrophages via MaCSF-1R

CSF-1 and CSF-1R have been well demonstrated in humans, regulating the differentiation, proliferation and survival of the mononuclear phagocyte system. However, the functional study on MaCSF-1 and MaCSF-1R from blunt snout bream (Megalobrama amblycephala) is still unknown. In the present study, we cloned and functionally characterized MaCSF-1 and MaCSF-1R. Multiple sequence alignment and phylogenetic tree analysis showed that both MaCSF-1 and MaCSF-1R were mostly close to the grass carp counterparts. Tissue distribution analysis showed that both MaCSF-1 and MaCSF-1R were widely distributed in all examined tissues, dominantly distributed in spleen, blood and head kidney tissues. Furthermore, confocal microscopy assay and flow cytometry assay showed that MaCSF-1R was the marker on the surface of macrophages. Recombinant MaCSF-1 promoted macrophage proliferation, phagocytosis and the production of IL-10. Through the pull-down experiments and indirect immunofluorescence experiments, the interaction between MaCSF-1 and MaCSF-1R was confirmed. To explore the relationship between MaCSF-1 and its receptor, MaCSF-1R and MaCSF-1R antibody was prepared. Then the MaCSF-1R blockage assay indicated that the role of MaCSF-1 on the macrophages proliferation and phagocytosis was weakened, leading the reduction of IL-10 expression level. In conclusion, MaCSF-1R is the marker on the surface of macrophage membrane; and MaCSF-1 promotes macrophage proliferation, phagocytosis, and significantly increased the expression levels of IL-10 depended on the interacting with MaCSF-1R. This study provides basal data for the biological function of MaCSF-1 and MaCSF-1R, and is valuable for the exploration of MaCSF-1 and MaCSF-1R molecular interactions.

Characterization of Pipefish Immune Cell Populations Through Single-Cell Transcriptomics

Teleost adaptive immune systems have evolved with more flexibility than previously assumed. A particularly enigmatic system to address immune system modifications in the evolutionary past is represented by the Syngnathids, the family of pipefishes, seahorses and seadragons. These small fishes with their unique male pregnancy have lost the spleen as an important immune organ as well as a functional major histocompatibility class II (MHC II) pathway. How these evolutionary changes have impacted immune cell population dynamics have up to this point remained unexplored. Here, we present the first immune cell repertoire characterization of a syngnathid fish (Syngnathus typhle) using single-cell transcriptomics. Gene expression profiles of individual cells extracted from blood and head-kidney clustered in twelve putative cell populations with eight belonging to those with immune function. Upregulated cell marker genes identified in humans and teleosts were used to define cell clusters. While the suggested loss of CD4+ T-cells accompanied the loss of the MHC II pathway was supported, the upregulation of specific subtype markers within the T-cell cluster indicates subpopulations of regulatory T-cells (il2rb) and cytotoxic T-cells (gzma). Utilizing single-cell RNA sequencing this report is the first to characterize immune cell populations in syngnathids and provides a valuable foundation for future cellular classification and experimental work within the lineage.

Transcriptome Profiling of Atlantic Salmon (Salmo salar) Parr With Higher and Lower Pathogen Loads Following Piscirickettsia salmonis Infection

Salmonid rickettsial septicemia (SRS), caused by Piscirickettsia salmonis, is one of the most devastating diseases of salmonids. However, the transcriptomic responses of Atlantic salmon (Salmon salar) in freshwater to an EM-90-like isolate have not been explored. Here, we infected Atlantic salmon parr with an EM-90-like isolate and conducted time-course qPCR analyses of pathogen load and four biomarkers (campb, hampa, il8a, tlr5a) of innate immunity on the head kidney samples. Transcript expression of three of these genes (except hampa), as well as pathogen level, peaked at 21 days post-injection (DPI). Multivariate analyses of infected individuals at 21 DPI revealed two infection phenotypes [lower (L-SRS) and higher (H-SRS) infection level]. Five fish from each group (Control, L-SRS, and H-SRS) were selected for transcriptome profiling using a 44K salmonid microarray platform. We identified 1,636 and 3,076 differentially expressed probes (DEPs) in the L-SRS and H-SRS groups compared with the control group, respectively (FDR = 1%). Gene ontology term enrichment analyses of SRS-responsive genes revealed the activation of a large number of innate (e.g. “phagocytosis”, “defense response to bacterium”, “inflammatory response”) and adaptive (e.g. “regulation of T cell activation”, “antigen processing and presentation of exogenous antigen”) immune processes, while a small number of general physiological processes (e.g. “apoptotic process”, development and metabolism relevant) was enriched. Transcriptome results were confirmed by qPCR analyses of 42 microarray-identified transcripts. Furthermore, the comparison of individuals with differing levels of infection (H-SRS vs. L-SRS) generated insights into the biological processes possibly involved in disease resistance or susceptibility. This study demonstrated a low mortality (~30%) EM-90-like infection model and broadened the current understanding of molecular pathways underlying P. salmonis-triggered responses of Atlantic salmon, identifying biomarkers that may assist to diagnose and combat this pathogen.

Full-Length Transcriptome: A Reliable Alternative for Single-Cell RNA-Seq Analysis in the Spleen of Teleost Without Reference Genome

Fish is considered as a supreme model for clarifying the evolution and regulatory mechanism of vertebrate immunity. However, the knowledge of distinct immune cell populations in fish is still limited, and further development of techniques advancing the identification of fish immune cell populations and their functions are required. Single cell RNA-seq (scRNA-seq) has provided a new approach for effective in-depth identification and characterization of cell subpopulations. Current approaches for scRNA-seq data analysis usually rely on comparison with a reference genome and hence are not suited for samples without any reference genome, which is currently very common in fish research. Here, we present an alternative, i.e. scRNA-seq data analysis with a full-length transcriptome as a reference, and evaluate this approach on samples from Epinephelus coioides-a teleost without any published genome. We show that it reconstructs well most of the present transcripts in the scRNA-seq data achieving a sensitivity equivalent to approaches relying on genome alignments of related species. Based on cell heterogeneity and known markers, we characterized four cell types: T cells, B cells, monocytes/macrophages (Mo/MΦ) and NCC (non-specific cytotoxic cells). Further analysis indicated the presence of two subsets of Mo/MΦ including M1 and M2 type, as well as four subsets in B cells, i.e. mature B cells, immature B cells, pre B cells and early-pre B cells. Our research will provide new clues for understanding biological characteristics, development and function of immune cell populations of teleost. Furthermore, our approach provides a reliable alternative for scRNA-seq data analysis in teleost for which no reference genome is currently available.

Transcriptome Profiling of Atlantic Salmon Adherent Head Kidney Leukocytes Reveals That Macrophages Are Selectively Enriched During Culture

The Atlantic salmon (Salmo salar) is an economically important fish, both in aquaculture and in the wild. In vertebrates, macrophages are some of the first cell types to respond to pathogen infection and disease. While macrophage biology has been characterized in mammals, less is known in fish. Our previous work identified changes in the morphology, phagocytic ability, and miRNA profile of Atlantic salmon adherent head kidney leukocytes (HKLs) from predominantly “monocyte-like” at Day 1 of in vitro culture to predominantly “macrophage-like” at Day 5 of culture. Therefore, to further characterize these two cell populations, we examined the mRNA transcriptome profile in Day 1 and Day 5 HKLs using a 44K oligonucleotide microarray. Large changes in the transcriptome were revealed, including changes in the expression of macrophage and immune-related transcripts (e.g. csf1r, arg1, tnfa, mx2), lipid-related transcripts (e.g. fasn, dhcr7, fabp6), and transcription factors involved in macrophage differentiation and function (e.g. klf2, klf9, irf7, irf8, stat1). The in silico target prediction analysis of differentially expressed genes (DEGs) using miRNAs known to change expression in Day 5 HKLs, followed by gene pathway enrichment analysis, supported that these miRNAs may be involved in macrophage maturation by targeting specific DEGs. Elucidating how immune cells, such as macrophages, develop and function is a key step in understanding the Atlantic salmon immune system. Overall, the results indicate that, without the addition of exogenous factors, the adherent HKL cell population differentiates in vitro to become macrophage-like.

A live attenuated Edwardsiella tarda vaccine induces immunological expression pattern in Japanese flounder (Paralichthys olivaceus) in the early phase of immunization

A previous study showed that an attenuated Edwardsiella tarda strain, TXhfq, as a live vaccine could elicit protective immune effects in fish against E. tarda infection. In the current study, in order to clarify the molecular mechanism of fish immune response at the early stage after TXhfq vaccination, RNA-Seq technology was used to compare the transcriptomes of skin, intestine, and spleen between bath-vaccinated and unvaccinated Japanese flounder (Paralichthys olivaceus). An average of 46.6 million clean reads per library was obtained, ~88.04% of which were successfully mapped to the reference genome, and approximately 24,600 genes were detected in each sample. A total of 565, 878, and 1258 differential expression genes (DEGs) were found in skin, intestine, and spleen, respectively, including 1263 up-regulated genes and 1438 down-regulated genes. The DEGs exhibited different characteristics in each tissue. One hundred and sixteen DEGs belonging to six immune related categories were scrutinized, i.e., inflammatory factors, cytokines, complement and coagulation system, mucins, phagocytosis, and antigen processing and presentation. A protein-protein interaction network was constructed to get the interaction network between immune genes during the early stage of immunization. The top six hub genes highly regulated by TXhfq formed complicated interaction relationship with each other, which were involved in immune processes, notably inflammation and phagocytosis. Our results provide valuable information for the understanding of the immune mechanism underlying the protection of live attenuated vaccines in fish.

Kinetics of T lymphocyte subsets and B lymphocytes in response to immunostimulants in flounder (Paralichthys olivaceus): implications for CD4+ T lymphocyte differentiation

CD4⁺ T lymphocytes play crucial roles in the adaptive immune system. CD4, as the most effective marker to delineate the T-helper subsets, was identified in many fish species. Two CD4 homologs, CD4-1 and CD4-2, have been reported in flounder (Paralichthys olivaceus). In this study, monoclonal antibodies (mAbs) against CD4-1 and CD4-2 of flounder were produced, CD4⁺ T lymphocytes were isolated and identified, and the variations in CD4⁺ and CD8⁺ T lymphocytes and IgM⁺ B lymphocytes after Poly I:C, PMA or β-glucan stimulation were investigated. Then, the expression of transcription factors and cytokines in sorted CD4⁺ T lymphocytes was analyzed. The results showed that the mAbs were specific to flounder CD4-1⁺ and CD4-2⁺ T cells. CD4-1⁺ and CD4-2⁺ cells responded to all three stimulants, while CD8⁺ T lymphocytes only give a strong response to Poly I:C, and the percentages of IgM⁺ B lymphocytes showed a tendency to increase. After stimulation, the expression of transcription factors and cytokines of Th1, Th2 and Th17 cells varied in CD4⁺ T cells. These results will provide crucial foundations for the differentiation and function of teleost CD4⁺ T lymphocytes.

Mudskipper interleukin-34 modulates the functions of monocytes/macrophages via the colony-stimulating factor-1 receptor 1

Interleukin-34 (IL-34) is a novel cytokine that plays an important role in innate immunity and inflammatory processes by binding to the colony-stimulating factor-1 receptor (CSF-1R). However, information on the function of IL-34 in fish remains limited. In the present study, we identified an IL-34 homolog from mudskippers (Boleophthalmus pectinirostris). In silico analysis showed that the mudskipper IL-34 (BpIL-34) was similar to other known IL-34 variants in sequence and structure and was most closely related to an orange-spotted grouper (Epinephelus coioides) homolog. BpIL-34 transcripts were constitutively expressed in various tissues, with the highest level of expression found in the brain. Edwardsiella tarda infection significantly up-regulated the mRNA expression of BpIL-34 in the mudskipper tissues. The recombinant mature BpIL-34 peptide (rBpIL-34) was purified and used to produce anti-rBpIL-34 IgG. Western blot analysis combined with PNGase F digestion revealed that native BpIL-34 in monocytes/macrophages (MOs/MФs) was N-glycosylated. In vitro, rBpIL-34 treatment enhanced the phagocytotic and bactericidal activity of mudskipper MOs/MФs, as well as the mRNA expression of pro-inflammatory cytokines like tumor necrosis factor α (BpTNF-α) and BpIL-1β in these cells. Furthermore, the knockdown of mudskipper CSF-1R1 (BpCSF-1R1), but not mudskipper BpCSF-1R2, significantly inhibited the rBpIL-34-mediated enhanced effect on MO/MФ function. In conclusion, our results indicate that mudskipper BpIL-34 modulates the functions of MOs/MФs via BpCSF-1R1.

Functional characterisation of interleukin 34 in grass carp Ctenopharyngodon idella

Interleukin (IL) 34 plays an important role in regulating macrophage functions and inflammation process. IL-34 homologues have recently been discovered in fish but the functions have not been studied. In this study, an IL-34 homologue was identified in grass carp Ctenopharyngodon idella and its bioactivities were investigated. The grass carp IL-34 was constitutively expressed in tissues, with the highest expression detected in spleen. It could be up-regulated in spleen after infection with F. cloumnare and grass carp reovirus II, and in primary head kidney leucocytes by recombinant IL-4/13B. The recombinant IL-34 produced in bacteria and HEK293T cells showed stimulatory effect on the expression of IL-1β, IL-6 and IL-8 but inhibited expression of IL-10 and TGF-β1 in primary head kidney macrophages. The results demonstrate that IL-34 is a proinflammatory cytokine in grass carp.

Oral delivery of Bacillus subtilis spores expressing grass carp reovirus VP4 protein produces protection against grass carp reovirus infection

Grass carp (Ctenopharyngodon idellus) hemorrhagic disease (GCHD), caused by grass carp reovirus (GCRV), has given rise to an enormous loss in grass carp industry during the past years. Up to date, vaccination remained to be the most effective way to protect grass carp from GCHD. Oral vaccination is of major interest due to its advantages of noninvasive, time-saving, and easily-operated. The introduction of oral vaccination has profound impact on aquaculture industry because of its feasibility of extensive application for fish in various size and age. However, the main challenge in developing oral vaccine is that antigens are easily degraded and are easy to induce tolerance. Bacillus subtilis (B. subtilis) spores would be an ideal oral vaccine delivery system for their robust specialty, gene operability, safety and adjuvant property. VP4 protein is the major outer capsid protein encoded by GCRV segment 6 (S6), which plays an important role in viral invasion and replication. In this study, we used B. subtilis spores as the oral delivery system and successfully constructed the B. subtilis CotC-VP4 recombinant spores (CotC-VP4 spores) to evaluate its protective efficacy in grass carp. Grass carp orally immunized with CotC-VP4 spores showed a survival rate of 57% and the relative percent survival (RPS) of 47% after the viral challenge. Further, the specific IgM levels in serum and the specific IgZ levels in intestinal mucus were significantly higher in the CotC-VP4 group than those in the Naive group. The immune-related genes including three innate immune-related genes (IL-4/13A, IL-4/13B, CSF1R), four adaptive immune-related genes (BAFF, CD4L, MHC-II, CD8), three inflammation-related genes (IL-1β, TNF-α, TGF-β) and interferon type I (IFN-I) related signaling pathway genes were significantly up-regulated in the CotC-VP4 group. The study demonstrated that the CotC-VP4 spores produced protection in grass carp against GCRV infection, and triggered both innate and adaptive immunity post oral immunization. This work highlighted that Bacillus subtilis spores were powerful platforms for oral vaccine delivery, and the combination of Bacillus subtilis spores with GCRV VP4 protein was a promising oral vaccine.

Distinct β-glucan molecules modulates differently the circulating cortisol levels and innate immune responses in matrinxã (Brycon amazonicus)

This study investigated the effects of two β-glucan molecules with different purities and isolated by different biotechnological processes on the immune response of matrinxã (Brycon amazonicus) prior and after challenge with Aeromonas hydrophila. In this sense, we evaluated serum cortisol and plasma glucose levels, the number of leukocytes (lymphocytes, neutrophils and monocytes), as well as the respiratory activity of leukocytes prior to, 6 and 24 h post infection (hpi). During 15 days, fish were fed with diets containing 0.1% of two β-glucans (β-G 1 and β-G 2, with 71 and 62% of purity, respectively) and then submitted to challenge. Results were compared with a positive control group fed with a β-glucan-free diet. A negative control group, also fed with β-glucan-free diet but inoculated with PBS, was established to evaluate the effect of handling during injection. Our results showed that different β-glucans affected differently the biological responses of matrinxã. The βG 2 modulated the cortisol profile prior to and after the acute infection with A. hydrophila, and increased the mobilization and activity of leukocytes. The infection promoted lymphopenia at 6 hpi and both β-glucans increased the circulating lymphocyte population 24 hpi. Moreover, the β-G 2 prevented the infection-induced neutrophilia at 6 and 24 hpi. Finally, the β-G 2 caused a marked increase in the circulating monocytes prior to infection, and a reduction at 6 hpi that was reversed at 24 hpi. In summary, our study demonstrates that β-G 2 was more efficient on the induction of the cell-mediate immunity in matrinxã.

Molecular characterization of a CC motif chemokine 19-like gene in ayu (Plecoglossus altivelis) and its role in leukocyte trafficking

The CC motif chemokine 19 (CCL19) functions in acute inflammation by recruiting lymphocytes and other cells. However, CCL19 has only been investigated in few fish species. In this study, we characterized a CCL19-like molecule (PaCCL19l) in ayu (Plecoglossus altivelis), a teleost fish. Sequence analysis revealed that PaCCL19l was most closely related to Atlantic salmon (Salmon salar) CCL19l1, which belonged to the fish CCL19a.1 subcluster. PaCCL19l was constitutively expressed in the tested ayu tissues and peripheral blood mononuclear cells (PBMCs), with the highest transcript level in PBMCs. Upon infection with Vibrio anguillarum, the expressions of PaCCL19l in the head kidney, liver, spleen, PBMCs, and monocytes/macrophages (MO/MΦ) were dramatically up-regulated. Recombinant PaCCL19l (rPaCCL19l) exhibited a significant effect on the chemotaxis of lymphocytes and MO/MΦ in vitro and in vivo. Meanwhile, rPaCCL19l exerted a high chemotaxic activity for lipopolysaccharide (LPS)-stimulated MO/MΦ (M1-type), but not for cyclic adenosine monophosphate (cAMP)-stimulated MO/MΦ (M2-type). When ayu MO/MΦ was treated with rPaCCL19l along with Vibrio anguillarum infection, the mRNA expression of proinflammatory cytokines (IL-1β, TNFα, IL-6, IL-12b, and IFN-γ) was up-regulated, while that of anti-inflammatory cytokines (IL-10, TGFβ, and IL-22) was down-regulated. Ayu MO/MΦ treated with anti-PaCCL19l IgG gave the opposite result. These results implicated that PaCCL19l is involved in the selective chemotaxis of ayu immune cells and promotes the host at a pro-inflammatory state.

The evolution of the macrophage-specific enhancer (Fms intronic regulatory element) within the CSF1R locus of vertebrates

The Csf1r locus encodes the receptor for macrophage colony-stimulating factor, which controls the proliferation, differentiation and survival of macrophages. The 300 bp Fms intronic regulatory element (FIRE), within the second intron of Csf1r, is necessary and sufficient to direct macrophage-specific transcription. We have analysed the conservation and divergence of the FIRE DNA sequence in vertebrates. FIRE is present in the same location in the Csf1r locus in reptile, avian and mammalian genomes. Nearest neighbor analysis based upon this element alone largely recapitulates phylogenies inferred from much larger genomic sequence datasets. One core element, containing binding sites for AP1 family and the macrophage-specific transcription factor, PU.1, is conserved from lizards to humans. Around this element, the FIRE sequence is conserved within clades with the most conserved elements containing motifs for known myeloid-expressed transcription factors. Conversely, there is little alignment between clades outside the AP1/PU.1 element. The analysis favours a hybrid between “enhanceosome” and “smorgasbord” models of enhancer function, in which elements cooperate to bind components of the available transcription factor milieu.

A transcriptome analysis focusing on inflammation-related genes of grass carp intestines following infection with Aeromonas hydrophila

Inflammation is a protective response that is implicated in bacterial enteritis and other fish diseases. The inflammatory mechanisms behind Aeromonas hydrophila infections in fish remain poorly understood. In this study, we performed a de novo grass carp transcriptome assembly using Illumina's Solexa sequencing technique. On this basis we carried out a comparative analysis of intestinal transcriptomes from A. hydrophila-challenged and physiological saline solution (PSS/mock) -challenged fish, and 315 genes were up-regulated and 234 were down-regulated in the intestines infected with A. hydrophila. The GO enrichment analysis indicated that the differentially expressed genes were enriched to 12, 4, and 8 GO terms in biological process, molecular function, and cellular component, respectively. A KEGG analysis showed that 549 DEGs were involved in 165 pathways. Moreover, 15 DEGs were selected for quantitative real-time PCR analysis to validate the RNA-seq data. The results confirmed the consistency of the expression levels between RNA-seq and qPCR data. In addition, a time-course analysis of the mRNA expression of 12 inflammatory genes further demonstrated that the intestinal inflammatory responses to A. hydrophila infection simultaneously modulated gene expression variations. The present study provides intestine-specific transcriptome data, allowing us to unravel the mechanisms of intestinal inflammation triggered by bacterial pathogens.

Molecular cloning, pathologically-correlated expression and functional characterization of the colonystimulating factor 1 receptor (CSF-1R) gene from a teleost, Plecoglossus altivelis

Colony-stimulating factor 1 receptor (CSF-1R) is an important regulator of monocytes/macrophages (MO/MΦ). Although several CSF-1R genes have been identified in teleosts, the precise role of CSF- 1R in ayu (Plecoglossus altivelis) remains unclear. In this study, we characterized the CSF-1R homologue from P. altivelis, and named it PaCSF-1R. Multiple sequence alignment and phylogenetic tree analysis showed that PaCSF-1R was most closely related to that of Japanese ricefish (Oryzias latipes). Tissue distribution and expression analysis showed that the PaCSF-1R transcript was mainly expressed in the head kidney-derived MO/MΦ, spleen, and head kidney, and its expression was significantly altered in various tissues upon Vibrio anguillarum infection. After PaCSF-1R neutralization for 48 h, the phagocytic activity of MO/MΦ was significantly decreased, suggesting that PaCSF-1R plays a role in regulating the phagocytic function of ayu MO/MΦ.

β-Glucan-induced cortisol levels improve the early immune response in matrinxã (Brycon amazonicus)

This study investigated the role of endogenous cortisol on the innate immune response in matrinxã (Brycon amazonicus) fed with β-glucan, prior to and after stressor exposure and bacterial challenge. For this, we evaluated the serum cortisol and plasma glucose levels, the serum lysozyme levels, the hemolytic activity of the complement system, and the respiratory activity of leukocytes, as well as the number of circulating erythrocytes and leukocytes of fish fed during 15 days with diets containing β-glucan 0.1% (β-G) or β-glucan 0.1% + metyrapone 30 mg kg^-1 fish (β-G + MTP). Dietary MTP was used to block cortisol production. After feeding, fish were air-exposed during 3 min, to endogenously increase the cortisol levels. Following that, they were challenged with intraperitoneal injection of Aeromonas hydrophila. Results were compared with a positive control group fed with a β-glucan-free diet. A negative control group, also fed with β-glucan-free diet but inoculated with PBS, was established to evaluate the effect of the handling during injection. Fish were sampled prior to the stressor exposure, 30 min after exposure, and 24 h post infection (hpi). Herein we observed that dietary β-G modulated the cortisol profile prior to and after the stressor, increasing the number and activity of leukocytes. Moreover, cortisol showed to be an efficient modulator of both humoral and cellular innate immune system by increasing lysozyme and complement activity, as well as neutrophil and monocyte populations. Our results suggest that β-glucan-induced cortisol increase is one important mechanism to improve the innate immune response in matrinxã.

Molecular characterization of an interleukin-4/13B homolog in grass carp (Ctenopharyngodon idella) and its role in fish against Aeromonas hydrophila infection

Mammalian interleukin 4 (IL-4) and interleukin 13 (IL-13) molecules are anti-inflammatory cytokines mediating the alternative activation of macrophages. However, the role of fish IL-4/13 homologs in monocytes/macrophages (MO/MФ) polarization remains unclear. In this study, we have functionally identified an IL-4/13B homolog in grass carp (Ctenopharyngodon idella), which is termed as CiIL-4/13B. Multiple alignment showed that CiIL-4/13B shared the typical characteristics and structure with other known fish IL-4/13. Phylogenetic analysis showed that CiIL-4/13B is evolutionarily closely related to zebrafish (Danio rerio) and common carp (Cyprinus carpio) IL-4/13B. CiIL-4/13B mRNA was constitutively expressed in tissues and peripheral blood lymphocytes (PBLs) examined, with its highest expression seen in PBLs. Following Aeromonas hydrophila infection, CiIL-4/13B mRNA expression was upregulated. Recombinant CiIL-4/13B (rCiIL-4/13B) was overexpressed in Escherichia coli and purified for a functional study. Using prepared anti-rCiIL-4/13B antiserum, Western blot analysis showed that native CiIL-4/13B in grass carp plasma is N-glycosylated. Intraperitoneal injection of bioactive rCiIL-4/13B significantly increased the survival rate of grass carp against A. hydrophila, and decreased the tissue bacterial load, with a higher dose having better effects. Bioactive rCiIL-4/13B treatment decreased nitrite production and mRNA expression of proinflammatory cytokines (IL-1β and TNF-α), while it increased arginase activity and mRNA expression of anti-inflammatory cytokines (TGF-β and IL-10). The phagocytosis by grass carp MO/MФ had no significant changes by the 8 h treatment of bioactive rCiIL-4/13B compared to that of the negative control, while it was significantly inhibited by the 24 h treatment of bioactive rCiIL-4/13B. The inhibitory effect of rCiIL-4/13B on MO/MФ phagocytosis may be a consequence of MO/MФ proliferation. In summary, our results suggest that CiIL-4/13B plays a protective effect in grass carp against A. hydrophila by inducing alternatively activated MO/MФ.

Cathelicidin modulates the function of monocytes/macrophages via the P2X7 receptor in a teleost, Plecoglossus altivelis

Cathelicidins (CATHs) are a family of endogenous antimicrobial peptides that are capable of both direct bacteria-killing and immunomodulatory effects. P2X7 receptor (P2X7R) is a mediator of CATH in mammalian immune cells. Here, we studied the function and regulation of CATH in head kidney-derived monocytes/macrophages (MO/MФ) from ayu, Plecoglossus altivelis. We investigated the chemotaxis of MO/MФ in response to ayu CATH (PaCATH), and found that PaCATH had a dose-dependent effect on MO/MФ chemotaxis with the optimal concentration of 10.0 μg/ml. The qPCR and Western blot analysis revealed that PaCATH inhibited the expression of ayu P2X7R (PaP2X7R) at both mRNA and protein levels. Knockdown of the PaP2X7R expression in ayu MO/MФ by RNA interference not only significantly inhibited the chemotactic effect of PaCATH on MO/MФ, but also obviously reduced the effect of PaCATH on the phagocytosis, bacteria-killing, respiratory burst, and cytokine expression of ayu MO/MФ. Our study revealed that the immunomodulatory effect of fish CATH is mediated by P2X7R.